Cancer cells employ complex and multifarious molecular mechanisms to overcome innate barriers that normally prevent runaway proliferation[1]. To address this complexity directly, we have pioneered the application of genome-wide siRNA screening to identify those gene products whose depletion has the most significant impact on paclitaxel sensitivity in Non-Small Cell Lung Cancer cells (NSCLC). This effort uncovered a collection of diverse candidates many of whom appear to be the products of anomalous gene expression programs and only impact mitosis in tumor cells. Using a stringent objective statistical algorithm and experimental validation, we have identified 3 novel and functionally diverse genes, whose role in mitosis has not previously been characterized. Because many of these genes display elevated expression patterns in tumors, we hypothesize that they may be tumor-cell specific dependencies for cell cycle progression. The purpose of this proposal is the mechanistic elaboration of the function of these genes with respect to their impact on mitosis and tumor growth in vivo. The long-term objective of this work is to deconstruct the components that are uniquely required for tumor cell mitosis. Ultimately, an understanding of how these proteins support mitosis will open new avenues for therapeutic intervention.